浮式鲆鲽类网箱在波流场中动态响应的数值模拟

根据浮式鲆鲽类养殖网箱的结构特点,基于有限元方法对波流共同作用下网箱的运动受力进行数值模拟,并将数值模拟结果与水槽模型实验结果进行比较分析。结果显示:在3种工况条件下,计算机模拟值与实验值吻合较好,验证了程序及数学模型的可靠性。借助于计算机3D可视化技术,可对波流场中网箱结构的运动过程进行虚拟呈现。其中,当流速为26cm/s时,网箱底框架最大倾角可达9°;波浪作用下底框架最大倾角为12°。当波流联合作用时,底框架最大倾角与最大锚绳受力值均高于波浪或水流单独作用时。当水流入射方向与波浪成角度时,底框架最大倾角与锚绳受力随着夹角的增加而减小。今后将通过海上实测进一步对模拟结果进行验证,使数值模拟能够更加精确。     

超大型结构物受波浪力作用的数值模拟

为了计算波浪效应下超大型结构物所受的波浪力,该文运用σ坐标变换来追踪随时间变化的自由液面,添加了浸没边界法(IBM)来处理不规则结构物表面,建立了基于大涡模拟(LES)方法的三维数值模型。为验证该数值模型的正确定,运用该模型来模拟规则波作用下大直径垂直圆柱的绕射问题,圆柱周围的波浪爬高数值解与解析解吻合良好。运用该三维数值模型,模拟了波浪与南京长江三桥南塔钢套箱相互作用的问题,数值计算出的结构物所受的波浪力与试验数据吻合良好,表明该数值模型能够很好地模拟工程中三维波浪与超大型结构物相互作用的问题。     

孤立波作用下圆柱桩波浪力计算方法研究EI北大核心CSCD

为研究孤立波作用下跨海桥梁桥墩受到的波浪荷载以得到孤立波波浪力的简化计算方法,利用计算流体力学软件OpenFOAM模拟海洋孤立波,在不同来流波高和初始水深下,开展了2组仿真试验,三维数值模拟用于直接计算圆柱体上的波浪力,二维数值模拟用于推导Morison方程所需的速度场。对比现有文献,讨论原始Morison方程应用于孤立波波浪力计算的适用性以及孤立波非线性的变化规律,并验证了引入非线性项的修正Morison方程预测孤立波荷载的适用性。研究结果表明:在计算孤立波荷载时,非线性影响不可忽视,随着波高和水深的比值H/d的增大,孤立波的非线性越来越强;相比原始Morison方程,考虑非线性影响的修正Morison方程可以更准确地预测孤立波与圆柱桩间的相互作用;应用修正Morison方程进行孤立波荷载预测时,波浪力参数C D,C M的取值与波高H、水深d、圆柱桩直径D的绝对值无关,仅与H/d有关;基于多组仿真试验结果,给出了0.15≤H/d≤0.65内波浪力参数的取值,可为孤立波荷载的快速计算提供参考。     

潜堤上孤立波传播的格子Boltzmann法数值模拟

基于格子Boltzmann法建立求解不可压缩的Navier-Stokes方程的数学模型,对孤立波与矩形潜堤和半圆形潜堤的相互作用过程进行了研究。通过建立二维数值水槽,采用Rayleigh推板造波,模拟了孤立波越过潜堤的过程。通过模拟速度场和自由表面,证明该模型能很好地模拟流动的分离和涡流的产生,结果与已有实验数据吻合。研究表明该模型能够模拟孤立波与潜堤相互作用中的水流分离、涡流产生、波浪破碎和传播等非线性现象。所得结论对于潜堤工程设计具有参考价值。     

直立堤上任意方向入射波的波压力研究

为了研究在不同入射波向时直立堤上的波压力,基于FLOW-3D,该文建立了三维数值波浪水池,并进行了物理模型试验。模型采用推板造波及孔隙消波的方法形成稳定的波浪场,数值模拟结果与试验结果吻合较好。研究表明:墙面测点的波压力与波吸力均随入射角度的增大而增大;墙底各测点浮托力的变化规律较为复杂,合田公式不能准确描述;墙面波压力的分布与合田公式基本相符;墙底浮托力的分布并不是合田公式描述的三角形,而是近似梯形分布;斜向波作用下的墙面波吸力分布图相似于正向入射时的分布。研究结论可为防波堤设计提供参考依据。     

基于有限元方法对波流场中养殖网箱的系统动力分析

养殖网箱系统在海中除承受静载荷以外还受到波流等动载荷的作用,为确保安全有必要对网箱系统进行动力分析。为此提出一种基于有限元原理的养殖网箱系统动力分析方法,分别对圆形重力式网箱在水流、波浪以及波流联合作用下的网衣变形与锚绳受力进行了数值模拟,并与实验结果进行了比较分析。结果表明:该方法具有解的稳定性,计算值与实验值比较吻合,较好地反映了网箱系统在波流场中的动力响应特性。     

带窄缝多箱体系统波浪荷载特性分析EI北大核心CSCD

针对波浪与带有窄缝多固定直角箱体结构作用产生的流体共振问题,建立了非线性波浪荷载分析二维时域模型。该模型采用域内源造波技术产生入射波浪,自由水面满足完全非线性运动学和动力学边界条件,窄缝内自由水面引入人工阻尼来等效由于涡旋运动和流动分离引起的粘性耗散,建立边界积分方程并采用高阶边界元离散求解物面上速度势等未知量,进而利用加速度势的方法来求得速度势时间导数,并基于伯努利方程积分得到作用结构上的瞬时波浪荷载。通过模拟带两窄缝的三箱体所受水平力与垂向力,并与已发表结果对比验证了模型的准确性。同时通过大量的数值计算,分析了箱体数量对各箱体所受波浪荷载大小及变化规律的影响。     

带窄缝多箱体系统波浪荷载特性分析

针对波浪与带有窄缝多固定直角箱体结构作用产生的流体共振问题,建立了非线性波浪荷载分析二维时域模型。该模型采用域内源造波技术产生入射波浪,自由水面满足完全非线性运动学和动力学边界条件,窄缝内自由水面引入人工阻尼来等效由于涡旋运动和流动分离引起的粘性耗散,建立边界积分方程并采用高阶边界元离散求解物面上速度势等未知量,进而利用加速度势的方法来求得速度势时间导数,并基于伯努利方程积分得到作用结构上的瞬时波浪荷载。通过模拟带两窄缝的三箱体所受水平力与垂向力,并与已发表结果对比验证了模型的准确性。同时通过大量的数值计算,分析了箱体数量对各箱体所受波浪荷载大小及变化规律的影响。     

防波堤帷幕尺度对波浪力和消浪性能的影响研究

帷幕式防波堤下部透水,利于港内外的海水交换,防止水质恶化,维持原始水域生态平衡,因此模拟波浪与防波堤的相互作用具有重要的现实意义。该文基于高阶紧致插值CIP(Constrained Interpolation Profile)方法的二维波浪数值模型水槽,通过与文献结果进行比较,结果表明：该文数值模型能够有效地模拟孤立波在冲击帷幕式防波堤过程中的波浪破碎等强非线性现象。通过数值模拟,描述了帷幕式防波堤在不同的宽度和浸没深度情况下与孤立波之间的相互作用中流速和涡度的演变过程,并讨论了孤立波波高和帷幕式防波堤结构尺寸对反射、透射、耗散系数以及在帷幕式防波堤上冲击力的影响。研究表明：帷幕式防波堤的相对浸没深度越大时,消浪效果良好,同时帷幕式防波堤的相对宽度对消浪效果的影响较大。     

造波理论在滑坡涌浪计算中的应用

波浪的产生可以由造波机在实验室生成,也可以是滑坡体滑入水中造成。它们具有相似性。本文根据造波理论,对滑坡体进行理想化假设,推导出滑坡涌浪计算方程。它能较准确的估算出滑坡涌浪高度,充分验证了造波理论在滑坡涌浪计算中的可行性。     

深水铰接塔平台的非线性动力特性分析

研究了铰接塔平台在波浪和海流作用下的非线性动力特性。将平台顶部工作单元简化为集中质量,塔柱和浮力仓简化为均匀直杆,建立了铰接塔平台动力分析模型。考虑海流和波浪对平台的作用,应用Morison公式计算铰接塔平台瞬时位置所受水动力,依据拉格朗日原理建立了铰接塔平台的强非线性运动方程。分别考虑波浪作用和波流联合作用,采用数值计算的方法研究了铰接塔平台超谐共振和混沌运动。研究表明,波流联合作用下平台的超谐共振运动响应增加,在大幅和较高频率波浪激励下,平台系统出现混沌运动。     

Numerical modelling of wave-induced currents in a breakwater situation

A numerical model system is developed to describe waves and wave-induced currents in a breakwater situation, where refraction, diffraction, reflection and wave–current interaction may all play important roles in the transformation of waves. A turbulence transport model is employed to estimate the eddy viscosity, and the friction factors associated with the major variables are clearly defined using a high level closure of combined flow bed friction. The model system is tested against a laboratory situation, and the effects of reflection are demonstrated on the wave-induced currents as well as on the wave distribution.     

Boundary element analysis of wave-current interaction around a large structure

A numerical approach for wave-current interaction around a large structure is investigated, based on potential flow theory, linear waves and small current velocity approximation. The velocity potential in a wave-current coexisting field is separated into a steady current potential and an unsteady wave potential. The boundary element method was then employed to compute the unsteady wave potential with effects of both a uniform current and a large body taken into consideration. It is demonstrated that the steady current potential can be expressed as the sum of a uniform current and a steady disturbance due to the presence of the object. The variation of current velocity in the vicinity of the object is then calculated by using a surface vorticity boundary integral meethod. Boundary element analysis is also used for the numerical solutions of the surface vorticity method. Substituting both unsteady wave potential and current velocity into the first-order dynamic surface boundary condition, the water surface elevation around a large structure in a wave-current coexisting field can then be obtained. Comparisons of numerical predictions with experimental results ar also made; qualitative good agreements are obtained.     

Experimental and numerical investigation of the effect of shock wave characteristics on the ejector performance

The entrainment performance and the shock wave structures in a three-dimensional ejector were investigated by Computational Fluid Dynamics (CFD) and Schlieren flow visualization. The ejector performance was evaluated based on the mass flow rates of the primary and secondary flows. The shock wave structures in the ejector mixing chamber were captured by the optical Schlieren measurements. The results show that the expansion waves in the shock train do not reach the mixing chamber wall when the ejector is working at the sub-critical mode. Decreasing of the shock wave wavelength increases the secondary mass flow rate. A three-dimensional CFD model with four turbulence models was then compared with the experimental data. The results show that the RNG k-ε model agrees best with measurements for predictions of both the mass flow rate and shock wave structures.     

基于小波变换的顶张力立管涡激振动规律实验研究

为研究顶张力立管在海流作用下的涡激振动规律,在大型波浪流水槽中进行涡激振动模型实验。实验中立管竖直固定于实验支架上,外部承受不同速度的流体作用,上端施加变化的顶张力。立管模型上均匀布置六个测点,根据每个测点布置的两个应变计,分别测得来流向和横向两个方向振动响应。通过小波变换方法对实验数据进行时间频域分析,得到立管涡激振动频率和振动幅值以及来流向与横向的耦合振动规律,考察顶张力变化对立管自振频率以及涡激振动的影响。     

Coupled boundary element and finite element model for fluid-filled membrane in gravity waves

This paper describes a three-dimensional, coupled boundary element and finite element model for dynamic analysis of a fluid-filled membrane in gravity waves. The model consists of three components, describing respectively, the membrane deflection and the motions of fluids inside and outside the membrane. Small amplitude assumptions of the surface waves and membrane deflection lead to linearization of the mathematical problem and an efficient solution in the frequency domain. A finite element model, based on the membrane theory of shells, relates the membrane deflection to the internal and external fluid pressure. Two boundary element models, which describe the potential flows inside and outside the membrane, are coupled to the finite element model through the kinematic and dynamic boundary conditions on the membrane. As a demonstration, the resulting model is applied to evaluate the dynamic response of a bottom-mounted fluid-filled membrane in a wave flume. Previous two-dimensional numerical model results and three-dimensional laboratory data verify and validate the present three-dimensional model. Analysis of the computed membrane response and surface wave pattern reveals intricate resonance characteristics that explain the discrepancies between the numerical model results and the laboratory data.     

Iceberg drift modelling and validation of applied metocean hindcast data

An iceberg drift model covering the Barents and Kara Seas has been developed. The skills of the model relies both on the ability to describe physical actions from the environment on the icebergs and the accuracy of the applied metocean variables (wind, waves and currents). Experiences from the East Coast of Canada show that iceberg modelling may work reasonably well and indicate that iceberg drift models are able to fulfil both of the above mentioned requirements. By applying similar models in other regions, it may be assumed that wind, waves and currents affect the iceberg in a similar way as at the East Coast of Canada. However, the reliability of available metocean data sources will vary significantly from region to region. Due to this, a study with the objective to evaluate the quality of the underlying metocean models has been performed.A significant amount of recorded wind, wave and current data from various regions in the Barents Sea have been applied in comparisons with hindcast data from selected atmospheric and oceanographic models. Results show that the quality of wind and wave data applied by the iceberg drift model is very good. Regarding current velocity, there is a poor match between data from the applied oceanographic model and measurements. A method for improving the current magnitude has been introduced.The relative importance of winds, waves and currents on iceberg drift has also been investigated. In general, currents are most important for iceberg drift. However, in open waters, the wave drift may become the most important forcing. The presented iceberg drift model is considered to provide good results in situations with strong winds (and waves) and low currents while situations with low winds will give less reliable results. It is concluded that the quality of incorporated metocean data in any iceberg drift model need to be documented in order to fully understand possible limitations in iceberg drift simulations. Further work should focus on improvements in oceanographic modelling in order to establish a more reliable oceanographic hindcast for the Barents Sea.